The present invention generally relates to a method and apparatus used to test the operational performance (i.e., for dynamometric testing) of an internal combustion engine under various ambient atmospheric pressures, thereby simulating operation of the engine at various altitudes. More particularly, the invention pertains to a method and apparatus that allow dynamometric testing of an internal combustion engine at various ambient atmospheric pressures, without requiring that the entire engine be enclosed within a barometric chamber of controlled pressure.
The following background information is provided to assist the reader in understanding the invention described and claimed herein. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation, unless specifically so indicated.
The manufacturers of modern vehicles powered by an internal combustion engine subject the vehicles to various testing procedures. One such testing procedure that is typically performed is xe2x80x9cdynamometric testingxe2x80x9d, which involves running the engine under actual or simulated likely-to-be encountered conditions, while simultaneously testing and measuring various parameters.
In one sense, an internal combustion engine can be viewed as an air pump that also produces rotational power. Accordingly, the characteristics and performance of an internal combustion engine can be significantly altered by a change in the ambient atmospheric pressure at which the engine is operated. For example, according to Boyle""s Law, air density varies directly with respect to atmospheric pressure and inversely with respect to atmospheric temperature, i.e., xcfx81(air density)=P/RT. Whereas a typical ambient atmospheric pressure at sea level is on the order of 100 kPa (i.e., kilopascals), a typical ambient atmospheric pressure in the location of Denver, Colo., U.S.A. is typically on the order of 80 kPa, or about 20% less that at sea level. With other factors remaining equal (e.g., ambient temperature and humidity), this results in an engine xe2x80x9cat altitudexe2x80x9d (e.g., in Denver) receiving a 20% less charge of oxygen with each intake stroke, given the same engine speed, throttle angle, EGR percentage, etc. Additionally, the internal combustion engines of most modern vehicles adjust, usually by software, the fuel delivery based on the ambient atmospheric pressure, sometimes directly measured, but usually estimated from other measured parameters. Accordingly, at altitude, the maximum power output of the engine can be significantly reduced.
Increasingly, the operation of a modern internal combustion engine vehicle is controlled by microprocessor software. Apart from the reduced maximum power output at altitude, there are a substantial number of factors in the vehicle""s software that are influenced by the ambient atmospheric pressure. For all of these reasons, it has been customary for vehicle manufacturers to dynamometrically (i.e., operationally) test their engines under conditions of varying atmospheric pressure. One manner in which vehicles have been traditionally tested under reduced atmospheric pressures is to actually operate the vehicles at altitude, e.g., in Denver, up Pike""s Peak, etc. For more preliminary testing, manufacturers have also used so-called xe2x80x9cdynamometric chambersxe2x80x9d. Such dynamometric chambers are closed barometric cells in which a lower than ambient pressure can be maintained. The engine is dynamometrically tested (run under various operating loads, conditions, etc.) within the chamber.
However, such dynamometric chambers can be expensive to build, operate and maintain. Since a rather large pressure differential must be maintained across the boundaries of the pressure cell, a dynamometric chamber is similar to a diving bell, requiring substantial and expensive structural support.
Accordingly, one objective of the present invention is the provision of a method and apparatus for the dynamometric testing of an internal combustion engine under varying ambient atmospheric pressures without requiring the building, operation or maintenance of a cumbersome and expensive barometric cell.
Another objective of the invention is the provision of a method and apparatus for the dynamometric testing of an internal combustion engine under varying ambient atmospheric pressures that is relatively inexpensive in construction and reliable in operation.
Yet another objective of the present invention is the provision of a method and apparatus for the dynamometric testing of an internal combustion engine under varying ambient atmospheric pressures which is, on the whole, safer than previously used barometric chambers, since pressures are controlled only across the inlet and output interfaces of the engine system, as opposed to over the entire surface of a dynamometric chamber. Therefore, the overall pressure-induced forces acting on the control surfaces are considerably reduced.
In addition to the objectives and advantages listed above, various other objectives and advantages of the invention will become more readily apparent to persons skilled in the relevant art from a reading of the detailed description section of this document. The other objectives and advantages will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein.
The foregoing objectives and advantages are attained by the various embodiments of the invention summarized below.
In one aspect, the invention generally features a method for conducting dynamometric testing of an internal combustion engine at a test site under a simulated atmospheric pressure that differs substantially from an actual ambient atmospheric pressure existing at the test site. The internal combustion engine has an air inlet for supplying an intake airflow for combustion within the internal combustion engine and an exhaust outlet for exhausting an exhaust flow exiting from the internal combustion engine. The method includes the steps of subjecting the air inlet to the simulated atmospheric pressure, subjecting the exhaust outlet to the simulated atmospheric pressure and operating the internal combustion engine while both of the air inlet and the exhaust outlet are subjected to the simulated atmospheric pressure.
In another aspect, the invention generally features an altitude simulator for dynamometer testing for conducting dynamometric testing of an internal combustion engine at a test site under a simulated atmospheric pressure that differs substantially from an actual ambient atmospheric pressure existing at the test site. The internal combustion engine has an air inlet for supplying an intake airflow for combustion within the internal combustion engine and an exhaust outlet for exhausting an exhaust flow exiting from the internal combustion engine. The altitude simulator for dynamometer testing includes an exhaust pressure controller for maintaining the exhaust outlet of the internal combustion engine substantially equal to a determined exhaust pressure during operation of the internal combustion engine and an intake pressure controller for maintaining the air inlet of the internal combustion engine substantially equal to a determined intake pressure during operation of the internal combustion engine.